1. Field of Invention
The field of the currently claimed embodiments of this invention relates to array structures, and more particularly to array structures of containers that have predetermined porosity.
2. Discussion of Related Art
It is a well-established practice in drug discovery, microbiology, tissue engineering and biotechnology to culture cells within microwell arrays (Charnley, M., Textor, M., Khademhosseini, A. & Lutolf, M. P. Integration Column: Microwell Arrays for Mammalian Cell Culture. Meg. Biol. 1, 625-634 (2009); Ma, B., Zhang, G., Qin, J. & Lin, B. Characterization of Drug Metabolites and Cytotoxicity Assay Simultaneously Using an Integrated Microfluidic Device. Lab Chip. 9, 232-239 (2009); Holmes, D. & Gawad, S. The Application of Microfluidics in Biology. Meth. Mol. Bio. 583, 55-80 (2010); Kim, L., Toh, Y. C, Voldman, J. & Yu, H. A Practical Guide to Microfluidic Perfusion Culture of Adherent Mammalian Cells. Lab Chip. 7, 681-694 (2007)). However, conventional microwell arrays do not accurately mimic the in situ cellular microenvironment due to a lack of three-dimensional (3D) cues from the external media thus generating physiologically compromised cells (Dutta, R. C. & Dutta, A. K. Cell-interactive 3D-scaffold; Advances and Applications. Biotech. Adv. 27, 334-339 (2009)). For example, due to limited access to the surrounding medium from only one opening (a single 2D interface) in traditional microwell arrays, hypoxic conditions resulting in decreased cell or tissue function have been reported (Rappaport, C. Review—Progress in Concept and Practice of Growing Anchorage-Dependent Mammalian Cells in Three Dimensions. In Vitro Cell Dev. Biol. 39, 187-192 (2003); Metzen, E. M., Wolff, J., Fandrey, J. & Jelkman, J. Pericellular pO2 and O2 Consumption in Monolayers. Respir. Phsyiol. 100, 101-110 (1991); Malda, J., Klein, T. J. & Upton, Z. The Role of Hypoxia in the In Vitro Engineering of Tissues. Tissue Eng. 13, 2153-2162 (2007)).
In numerous lab-on-a-chip applications where a small device size is desirable while retaining high perfusion with the surrounding medium, there is a need to transition to the third dimension. For example, to increase diffusion of media in cell culture devices, researchers have developed microfabricated chemostats with porous side walls, see A. Groisman, et al., Nat. Methods 2:685-689 (2005), partitioned microfluidic channels, see A. P. Wong, et al., Biomaterials 29:1853-1861 (2008), and microgel-based building blocks. See Y. Du, et al., Proc. Nat. Acad. Sci. USA 105:9522-9527 (2008). As compared to gel-based systems where porosity is a consequence of crosslinking and can have considerable spatial variability, lithographic patterning of pores offers the possibility for high precision and reproducibility. See T. A. Desai, et al., Biotechnol. Bioeng. 57:118-120 (1998). Although lithographic approaches have been successfully applied to microfabricated containers, in most cases, however, they feature porosity in inherently two-dimensional (2D) geometries, which allow diffusion only from the top and bottom faces. See J. Kwon, et al., J. Vac. Sci. Technol., B, 27:2795-2800 (2009); S. L. Tao, et al., Nat. Protocols 1:3153-3158 (2007). There thus remains a need for improved sub-centimeter array structures that have selectable porosities.